Minerals and Rocks

Rocks

• Aggregates (mixture—can be separated) of minerals.

Minerals

• Four Characteristics:– Naturally occurring– Inorganic (was never

alive)– Solid– Possesses a definite

chemical structure

Properties of Minerals

• Crystal form—external expression of internal structure

Properties of Minerals

• Color—unreliable in identifying minerals

Properties of Minerals

• Streak—the color of a mineral in its powder form—obtained by rubbing the mineral across a hard, unglazed porcelain

Properties of Minerals

• Hardness—resistance of a mineral to abrasion or scratching– Mohs scale—hardness

scale ranging from 10 (hardest) to 1 (softest)

– Diamond is 10, talc is 1

Properties of Minerals

• Cleavage—tendency of a mineral to break along planes of weak bonding

Properties of Minerals

• Fracture—do not exhibit cleavage when broken

• Specific gravity—the weight of a mineral compared to the same volume of water

Mineral Groups

• Silicates– Silicon and oxygen are the two

most abundant elements in the Earth’s crust; they form silicates

– All have the same basic structure—the silicon-oxygen tetrahedron—four oxygen atoms surrounding a silicon atom

– Other elements join the tetrahedrons together in chains, sheets, or three-dimensional networks.

– Feldspars are most abundant, with quartz second

Mineral Groups

• Carbonates– Calcite

• Limestone—used in building and paving

• Marble—used decoratively

• Halite (salt) and Gypsum also found in sedimentary rock

Mineral Resources

• Reserves—already identified deposits from which minerals can be extracted profitably

• Ores—useful metallic minerals that can be mined at a profit

• Changing economic factors determine whether a deposit is profitable to extract